Patients 21 years old and older with essential tremor may be eligible for this study. Participants are admitted to the NIH Clinical Center for two treatment periods of 1 week each, with a 1-week break at home between treatments. Before beginning treatment, participants undergo a medical history, physical examination, blood and urine tests, and an electrocardiogram (EKG). In addition, tremors are measured using accelerometry, a procedure in which a small device, mounted on a piece of cardboard, is taped to the patient's hand for about 30 minutes.